Today my 78-year-old mother got back on a bike for the first time in around 15 years. She had a bit of the wobblies at first but settled into it pretty quickly. Nice and flat, car-free side streets around her house, and I lowered the seat on her old Humber 3-speed so she can put her feet down easily (insert 'granny bike' pun here).
Ok, I'm a little nervous for her, since she didn't really ride much as a kid. But this is the same woman who started playing the cello at age 57, so I'm sure she'll be fine. It'll be good for her hip that's gotten a little funky.
Still, keep it in first gear for a while, mom.